The present invention relates to a method and a system for transferring a supervisory right requirement signal between stations in a submarine cable communication network system.
In a submarine cable communication network system, a plurality of stations are connected to each other through submarine cables including repeaters. In the system, each of stations periodically supervises repeaters connected thereto through submarine cables to trouble shoot the repeaters and/or to perform maintenance of the repeaters and the cables. In the supervisory action, each of the stations commands the repeaters to send to the station routine data or specific data measured in the repeaters. When some of the stations carry out the supervisory action for a single repeater at the same time, the supervising is confused due to collision of supervisory action. In order to avoid the confusion, a particular one of the stations can perform the supervisory action to repeaters after acquiring a supervisory right for repeaters by use of different signals representative of the supervisory right requirement individually assigned to the stations. The different signals are collectively referred to as a supervisory right requirement signal or a supervisory action flag signal. The supervisory right requirement signal usually has a digital data signal format and includes a station address assigned to the particular station requiring the supervisory right. During a time duration when the particular station holds the supervisory right and performs the supervisory action onto the repeaters, the other stations can neither acquire the supervisory right nor perform the supervisory action onto the repeaters. When the particular station completes the supervisory action onto the repeaters, the particular station abandons the supervisory right. Then, the supervisory right becomes neutral so that the supervisory right is left in the condition where any one of the stations is possible, as the particular station, to acquire the supervisory right by transmitting the supervisory right requirement signal.
Those stations are arranged in a circular loop for transferring the supervisory right requirement signal one after another as from one station to an adjacent station through submarine cables between adjacent stations. When a particular one of the stations desires to acquire the supervisory right, the particular station sends out the supervisory right requirement signal assigned thereto to the adjacent one of the stations. The supervisory right requirement signal is circulated through the loop and returns to the particular station. After confirmation of the return, the particular station acquires the supervisory right. Then, the particular station performs the supervisory action onto the repeaters and does not relay the supervisory right requirement signal from one to another of the stations adjacent to the particular station in the loop, even if the particular station would receive the supervisory right requirement signal from the adjacent one of the stations. Thus, any other stations cannot acquire the supervisory right. Upon completion the supervisory action, the particular station abandons the supervisory right and is in a condition to relay the supervisory right requirement signal from one to the other of the opposite adjacent ones of the stations.
In a conventional system using a transferring circular loop, it is impossible to transfer the supervisory right requirement signal when any fault occurs in the circular loop, for example, any one of cables is broken. As a result, any one of stations cannot acquire the supervisory right. Usually, a public line is used as a back-up line, but the supervisory right cannot be acquired by any stations if there is no public telephone line.